Double check yourself, before you double wreck yourself. Make sure everything you send to a company, whether a résumé, an email or a portfolio, is good to go. Double check your grammar and wording, and for God’s sake use spell check! This is especially important when it comes to the company’s name. Don’t spell their name wrong and be sure to type it how they type it (e.g. Problogger, not Pro Blogger).
If you have to pay it now, you have to take out a loan, ask for an advance on your salary or borrow money from friends or family. If it can wait, the amount will accumulate interest until you pay it back. If it's just one month out of twelve, and the other eleven you always have money left over, there's not really anything to worry about. Put the left over money aside to pay this month's expenses. Other than that, there are only two things you can do: spend less, or earn more. Sell your car, move to a smaller place, get a roommate. Cut whatever expenses you need to break even. Try for a second job, a raise, or sell something you make.
Now, unfortunately, there are a lot of scams when it comes to GPT sites. So it’s best to stick with well known, trusted sites that have been around for a while. You don’t want to complete offers for a month then when it’s time to cash out your earning find out that the site no longer exist. Trust me, I have seen a lot of “here today, gone tomorrow” rewards sites.